U.S. Pat. No. 4,978,387 discloses a typical method for manufacturing molten pig iron using raw iron ore and coal without carrying out pre-treatments.
According to this U.S. patent, a raw iron ore and coal are directly used, so that pre-treating steps such as sintering and coking can be skipped unlike in the other blast furnaces, thereby simplifying the process steps and the manufacturing facilities.
As illustrated in FIG. 1, the apparatus 400 of U.S. Pat. No. 4,978,387 includes: a melter-gasifier 410 for gasifying the coal and for melting a reduced iron; a packed bed type Dre-reducing furnace 432 for indirectly reducing the iron ore by using a reducing gas produced by the melter-gasifier 410; and other auxiliary facilities.
The auxiliary facilities include: a cyclone 411, a recycling device 412, a melter-calciner 413, and venturi scrubbers 433 and 434.
Within the melter-gasifier 410, the coal is gasified to produce a reducing gas for indirectly reducing the iron ore. Further, it utilizes the generated heat to melt the reduced iron which has been indirectly reduced by the pre-reducing furnace 432. Meanwhile, the pre-reducing furnace 432 uses the reducing-gas of the melter-gasifier 410 to indirectly reduce the raw iron ore and the additives. The reduced iron thus produced is continuously discharged to be charged into the melter-gasifier 410.
In this method, however, the raw material can be used in the form of agglomerates (8-35 mm), and therefore, a limit is encountered in the raw material. That is, over 80% of the production of iron ore in the world is fine iron ore, but the above facility can use only lump iron ore and the expensive pellets, this being a serious disadvantage.
Meanwhile, U.S. Pat. No. 5,192,486 discloses a direct iron ore reducing apparatus which uses fine iron ore.
As shown in FIG. 2, this apparatus 500 includes: a fluidized bed type pre-heating furnace 544 for pre-heating the iron ore by means of a hot air which has been heated by a combustion chamber 547; 3-stage reducing furnaces 541, 542 and 543; a gas reformer 545 for producing a reducing gas; a heat exchanger 546 for heating the gas reformer 545; gas cleaning scrubbers 549 and 550; and a briquetting device 516.
The gas reformer reforms a natural gas to produce a reducing gas for reducing the iron ore. Then the reformed gas is heated by the heat exchanger 546 to be supplied to a final reducing furnace 541. The reducing gas sequentially passes through a second pre-reducing furnace 542 and a first pre-reducing furnace 543 to be cleaned by the gas cleaning scrubber 549 so as to be circulated by going through the heat exchanger 546. The fine iron ore is fed into the pre-heating furnace to be pre-heated, and then, sequentially passes through the first pre-reducing furnace 543, the second pre-reducing furnace 542 and the final reducing furnace 541 to be finally reduced. The reduced iron is agglomerated by the briquetting device 516 into briquettes.
The above described facility uses natural gas, and requires 4-stage fluidized bed type furnaces. Thus the facility is extremely complicated, and therefore, the initial facility cost is high, while the operation is also very complex.